Enhancing the performance of low molar ratio urea–formaldehyde resin adhesives via in-situ modification with intercalated nanoclay

Low molar ratio urea–formaldehyde (UF) resin adhesives are primarily used for the reduction of formaldehyde emission (FE) from wood-based composites, at the expense of poor reactivity and adhesion. This study aimed to enhance the performance of low molar ratio UF resins via in-situ modification, via the addition of octadecylamine (ODA)-modified bentonite (ODA–BNT) nanoclay. The molecular weights, curing behavior, chemical groups, and crystallinity of modified UF resins with different levels of ODA−BNT were characterized by gel permeation chromatography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and X-ray diffraction (XRD). The ODA–BNT/UF resins showed better reactivity and lower activation energy compared with neat resins. The XRD results clearly showed that ODA–BNT in modified UF resins had been intercalated. A 5% ODA−BNT addition resulted in a decrease in the crystallinity of the modified UF resins, leading to better adhesion strength and lower FE compared with neat UF resins. These results suggest that intercalation of ODA–BNT in low molar ratio UF resins improve their cohesion through the formation of a larger branched network in their cured state.